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User blog:DocTanner/Comprehensive note on landing gear
Note: This blog post is taken from the similar forum post, here. It'll be kept up-to-date as the forum post progresses. Feel free to comment in either location. Introduction Hello. Since landing gear have come out, I've seen a lot of discussion about how they work, why they're buggy, how to use them, etc. I'd like to take a minute to address the issues I've seen and try to shed a little light on the subject. Breaking The biggest issue with landing gear is their tendency to be destroyed while travelling. For example, say you build a carrier and dock a bunch of fighters to it. You take off for your space dock with no problems. As you arrive, you turn off thrusters so you can slow to a stop and suddenly your fighters tear free of the deck and mass into the front wall of the hangar. Why does this happen? Inertia. When you have a single ship, the forces from your thrusters and gyros are applied to all parts of it equally. So, the whole ship moves and turns as one. When you have a magnetically latched ship, however, this isn't true. As the carrier maneuvers, the inertia of the fighters applies a force to the landing gear. If the force is large enough, the landing gear can be destroyed. Think back to highschool physics. Remember f=ma? Force equals mass times acceleration. We can use that formula to take a look at exactly what happened to your fighters: * When you started your trip, your carrier and fighters were both stationary. You fire your aft thrusters and, since it's a manual burn, they kick in at 2:3 max power. * As you get up to speed, force is applied to your landing gear equal to the mass of the fighter times the acceleration of the ship. Depending on how they're docked, this might be a sheer, compression, or tension force. (This is important later) * While you're travelling at the carrier's maximum speed, you're no longer accelerating. So no force is applied to the landing gear. * When you try to stop, your fighters are still moving forward. Your reverse thrusters kick in to slow you down. Keep in mind that deceleration is just acceleration in opposite direction, so the equation is exactly the same. However, the reverse thrust is at full power. * The fighters' mass is the same, but the acceleration is 1.5x faster than before, so the applied force is 1.5x larger. This time, the landing gear can't take the increased force and snap. Now free of their moorings, your fighters smash into the front bulkhead. (More accurately, your bulkhead smashes into them... but it's all a matter of reference frame.) If you're still confused, that's okay. Imagine you're driving a car instead. In this analogy, the car is like the carrier and you are like the fighters. As the car accelerates, you are pressed back into the seat. The force applied isn't too much though, and everything is fine. Once you're up to speed on the highway, you don't feel any force at all. Until... BAM, you hit a deer. Suddenly the car decelerates far more rapidly than it would on it's own. From your perspective, it's accelerating away from you backwards. That acceleration, times your mass, is the force applied between you and the seatbelt. With enough acceleration, you'll break through the seatbelt and hit the windshield. Or, again, more accurately, the windshield will hit you. So what can you do to stop your ships from breaking free and wrecking your flight deck? * Install more landing gear. The more there are, the more the force can be spread out and kept below the breaking point. * Change the angle of force. As far as I can tell, landing gear are far stronger under compression and tension forces than they are under sheer forces. Essentially, they can take more crushing and stretching than they can sliding. Keep in mind, that this doesn't solve the problem. Rotating, strafing, ascending and descending can still apply sheer force. * Accelerate gently. Don't rapidly change speed or direction. Install fewer thrusters, be gentle on turning, etc. This will stop your docked ships from breaking loose, but take you longer to go from place to place. Inertial Dampers So you've redesigned and rebuilt all your fighters to handle acceleration while docked. You've repaired your hangar. Finally, you're ready to try again. Confident everything is going to hold fast, you head to the carrier's bridge and fire up aft thrusters to full. A few explosions later, you've got a hole in your back wall and you're flying away from the wreckage of your fastest fighter. What happened? How did it tear free and why did it do so much damage on the way out your hull? They just bounced around inside before, what changed? You forgot to turn the fighter off. Inertial dampers are smart: they'll work with or without you. Gyros kick in automatically to kill rotational velocity while thrusters burn at full power to cancel translational velocity. This system is great for helping you sit at one point in space without drifting. Unfortunately, it's REALLY good at it. As soon as you started moving in the carrier, your fighter's engines came on at full burn to try and bring it to a stop. Your landing gear may have been able to handle the force from acceleration, but the fighter's thrusters tossed on an extra couple million Newtons. Boom, no more landing gear. The back wall of the hangar didn't fare too much better, either. Next time, you've got two options: * Turn off the inertial dampers of parked ships. This is done with the 'x' button in the default keybindings and will leave you with the warm glow of your thrusters in the hangar bay. Unfortunately, it doesn't always get saved properly, so you'll have to check all your fighters each time you load your world. * Turn off reactors. Press the 'y' button and shut down all power to the fighter. Without powered thrusters and gyros, it can't fight back. Of course, you've also lost your lights, but that's a small price to pay. Don't worry, the magnetic locks on your landing gear will still work. Rotation Finally, everything is patched up, all your fighters are offline, and you're ready to go. You even moved your hangar bay to the bottom of your carrier, just in case. Back up to the bridge, aft thrusters to full and... the nose drops? You keep trying, but for some reason, every time you try to fly forward, you start to dive foward. Now what? Well, once again inertia is not your friend. There's an excellent forum post on this subject, here. So, I won't go into to too much detail. But, basically, your ship is designed to fly in a straight line given its mass and geometry. Call it "calibrated thrusters" or something. Regardless of how it works, when you push forward, you go forward. It doesn't matter where the thrusters are. However, when you've got something clamped to your hull, its mass and geometry isn't taken into account. You didn't have an issue before, because your hangar was in line with your thrusters. But now that you've moved it lower, suddenly it causes you to curve. Why? Well... imagine your ship broken into three sections: top, middle, and bottom. When it's empty, all three sections are being pushed forward equally. And if extra mass is applied to the center, it doesn't unbalance you one way or the other. But add it at the top, or at the bottom, and you've got yourself a see-saw. Here's an experiment you can try right at your desk: * Grab a pencil and a small weight - a quarter works perfectly. (Non-US folks, any heavy coin or small object will do.) * Lay the pencil on the desk and use the tip of your finger to push it from the side, right in the middle. For this to work properly, make sure you are pushing it without grabbing it. Putting the tip of your finger on the table and sliding it from there works well. * Without the weight, the pencil should slide (or roll) perfectly straight. * Now put the weight next to the pencil, again right in the middle, and push from the opposite side. The pencil still goes straight, pushing the weight right along with it. * Move the weight away from the middle of the pencil and try again. Now when you push from the middle, the pencil spins around the weight instead of pushing it. Basically, that's exactly what is happening to your ship. So, how do you fix it? Well, we can use the same experiment to figure out a solution: * This time, use two fingers -- spread apart -- to push the pencil. * Without the weight, you'll notice that you can pretty much push from any two points and have it go straight. (The physics here breaks down slightly, due to friction from the table, but it should work.) * Put the weight back, anywhere between your fingers. Again, it goes straight. No matter where the weight or fingers are, so long as it's between them, the pencil goes straight. * Move the weight somewhere to the left or right of both fingers. Voila, again with the spinning. No matter what you do, the pencil just pivots on the closest finger, just like before. So how to use this to solve our nose-diving carrier problem? All you have to do is make sure that all your cargo, fighters, etc is between your thrusters. It doesn't have to be perfectly balanced, but it needs to be balanced enough so that your thrusters and gyros can compensate from the mass. As a general rule of thumb, imagine a the shape formed if you drew lines connecting all your thrusters together. All magnetically-connected cargo should be within this shape. The more centered the load, or the more powerful your thrusters, the better off you'll be. But if you're outside that shape, it's impossible for the thrusters to compensate by themselves. Check out that other forum post and play around with it for yourself to find what works. If you build something that constantly turns when you try to move forward, you probably need to build out in the direction you're rolling and add a couple thrusters. Stay tuned... That's all for now. Let me know in the comments below if you have any other issues you'd like me to address, or if you still have any questions. I'll continue updating this post so long as I have things to write about Category:Blog posts